Rotary drilling methods employing a drill bit and drill stems have long been used to drill well bores in subterranean formations. Drilling fluids or muds are commonly circulated in the well during such drilling to cool and lubricate the drilling apparatus, lift cuttings out of the well bore, and counterbalance the subterranean formation pressure encountered. The specific gravity of a well fluid is normally adjusted in such a way that the pressure of the fluid on the rock formations exceeds the formation pressure on the well. As a result, liquid components of the well fluid are forced into the formation surrounding the well while insoluble components settle on the walls of the well in the form of a stabilizing “filter cake.”
In drilling a well, the path followed by the drill pipes may intentionally or unintentionally deviate from the vertical. At such consequent deviations from vertical, the rotating drill pipes may come into contact with the filter cake and even with the wall of the well. In such instances, differential jamming or sticking of the drill pipe can occur when the rotation of the drill pipe is stopped. Once differential sticking occurs, the drill sting can not be raised, lowered or rotated and the well must be either abandoned or the drill string must be unstuck. One of skill in the art will appreciate that the jamming or sticking of the drill pipe is often the result of the drill pipe being forced into the wall of the well by the hydrostatic pressure of the column of mud. The contact surface between the drill pipe and the filter cake/wall of the well is then isolated from the mud pressure. If, as is usually the case, the mud pressure is greater than the formation pressure, the drill pipe is held fast to the wall by the pressure differential. It is well known that the pressure differential increases with the thickness and compressibility of the filter cake. With time, even relatively large sections of the drill pipe can become held fast, especially in extended reach or substantially horizontal well drilling operations.
In order to free stuck pipe, prior art treatments involve the placement in and movement through the circulating mud system a volume of release agent, know as spotting fluids. Spotting fluids need a good lubricating effect and the ability to ensure good oil wettability of the surfaces of the drill pipe and of the walls of wells coming into contact with the drill pipe. One commonly used method to release stuck pipe is the use of a “spotting” fluid in the hole opposite the stuck section of pipe. The spotting fluid may penetrate between the mud cake and pipe lubricating the area between the pipe and borehole resulting in less friction and quicker release. More often than not, an extensive period of time is necessary for this to occur, which results in an expensive loss of rig time.
One of skill in the art should understand and appreciate that the formulation and use of spotting fluids in water based drilling fluids is well known. For example see U.S. Pat. Nos. 4,466,486; 4,494,610; 4,614,235; 4,631,136; 4,964,615; 5,120,708; 5,141,920; 5,247,992; 5,645,386; 5,652,200; 5,945,386; 6,435,276; 6,524,384; and H1000.
The same cannot be said for spotting fluids for use in oil based drilling fluids. Typically, when oil based drilling fluids are used differential sticking is less of a concern. However, with extended reach wells and extensive horizontal drilling, even with oil based drilling fluids, differential sticking has become a problem. Thus there remains a need for the development of environmentally friendly spotting fluids for use in oil based drilling fluids.